Throughout the application various publications are referenced in parentheses. The disclosures of these publications in their entireties are hereby incorporated by reference in the application in order to more fully describe the state of the art to which this invention pertains.
1. The Field of the Invention
This invention relates to the medical arts. In particular, it relates to a method of enhancing the delivery of a medicant across abnormal microvasculature to a tissue requiring treatment.
2. Discussion of the Related Art
Pathologic neovascularization, i.e., the proliferation or development of new blood vessels, is essential for the growth and spread of primary, secondary and metastatic malignant tumors. It is known that certain properties of the new capillaries and arterioles constituting the neomicrovasculature in solid tumors differ from those of normal microvasculature. (J. Denekamp et al., Vasculature and microenvironmental gradients: the missing links in novel approaches to cancer therapy?, Adv. Enzyme Regul. 38:281–99 [1998]). Neomicrovasculature induced by angiogenic factors from malignant cells was reported to possess altered pharmacological reactivity to some vasoconstricting agents, compared with neomicrovasculature that was not induced by neoplastic cells. (S. P. Andrade and W. T. Beraldo, Pharmacological reactivity of neoplastic and non-neoplastic associated neovasculature to vasoconstrictors, Int. J. Exp. Pathol. 79(6):425–32 [1998]).
A number of proposed cancer treatments have been based on differences between neomicrovasculature and normal microvasculature. For example, combretastatin A-4 was shown to cause vascular damage and occlusion selectively in the blood vessels of malignant tumors compared to normal blood vessels. (G. G. Dark et al., Combretastatin A-4, an agent that displays potent and selective toxicity toward tumor vasculature, Cancer Res. 57(10): 1829–34 [1997]; D. J. Chaplin et al., Anti-vascular approaches to solid tumour therapy: evaluation of combretastatin A4 phosphate, Anticancer Res. 19(1A):189–95 [1999]). Monoclonal antibodies have been directed to antigens and antigenic combinations specific to endothelial cells of pathologic neovasculature, such as vascular cell adhesion molecule (VCAM)-1, phosphatidylserine (PS), the glycoprotein endosialin, and prostate-specific membrane antigen (PSMA), with the aim of selectively inducing thrombosis in neovasculature. (E.g., S. Ran et al., Infarcation of solid Hodgkin's tumors in mice by antibody-directed targeting of tissue factor to tumor vasculature, Cancer Res. 58(20):4646–53 [1998]; I. Ohizumi et al., Antibody-based therapy targeting tumor vascular endothelial cells suppresses solid tumor growth in rats, Biochem. Biophys. Res. Commun. 236(2):493–96 [1997]; S. S. Chang et al., Five different antiprostate-specific membrane antigen (PSMA) antibodies confirm PSMA expression in tumor-associated neovasculature, Cancer Res. 59(13):3192–98 [1999]; W. J. Rettig et al., Identification of endosialin, a cell surface glycoprotein of vascular endothelial cells in human cancer, Proc. Natl. Acad. Sci. USA 89(22):10832–36 [1992]). But taken alone, shutting down blood flow through the neomicrovasculature to malignant tumors may not necessarily result in stopping tumor growth, because actively proliferating populations of neoplastic cells at the periphery of solid tumors may have access to blood supplied by normal microvasculature. (E.g., D. J. Chaplin et al. [1999]).
Consequently, other conventional and novel therapeutic modalities will continue to be of value in the treatment of malignant, solid tumors. However, the efficacy of novel therapeutic agents, including cytotoxic chemotherapeutic agents, monoclonal antibodies, cytokines, effector cells, and viral particles has been limited by their ability to reach their targets in vivo in adequate quantities. (E.g., R. K Jain, Vascular and interstitial barriers to delivery of therapeutic agents in tumors, Cancer Metastasis Rev. 9(3):253–66 [1990]). An important limiting factor is the low permeability to macromolecules and viral particles of neomicrovasculature supplying the tumors.
This problem of microvascular permeability is especially acute with respect to malignant tumors of the central nervous system. These malignancies are usually fatal, despite recent advances in the areas of neurosurgical techniques, chemotherapy and radiotherapy. In particular, there are no standard therapeutic modalities that can substantially alter the prognosis for patients with malignant tumors of the brain, cranium, and spinal cord. For example, high mortality rates persist for patients diagnosed with malignant medulloblastomas, malignant meningiomas, malignant neurofibrosarcomas and malignant gliomas, which are characterized by infiltrative tumor cells throughout the brain. Although intracranial tumor masses can be debulked surgically, treated with palliative radiation therapy and chemotherapy, the survival associated with intracranial tumors, for example, a glioblastoma, is typically measured in months. The development of new therapeutic modalities against solid brain tumors largely depends on transvascular delivery of the potential therapeutic agent.
Transvascular delivery of chemotherapeutic agents and viral particles to tumor cells or other abnormal brain tissue is hampered by the blood-brain barrier, particularly the blood-tumor barrier found in brain tumors. The blood-brain barrier is a transvascular permeability barrier thought to result from the interendothelial tight junctions formed by the cerebrovascular endothelial cells of brain capillaries and arterioles in both normal and abnormal brain tissue. The blood-brain barrier protects the brain from changes in the composition of the systemic blood supply (e.g., in electrolytes) or from blood-borne macromolecules, such as immunoglobulins or other polypeptides, and prevents the transvascular delivery of many exogenously supplied pharmaceutical agents to brain tissues.
The treatment of brain tissue abnormalities, such as tumors, often involves the use of pharmaceutical agents with a significant toxicity of their own, making it highly desirable to be able to preferentially direct such agents to the abnormal or malignant tissue. While, there has been a great deal of interest in developing techniques which are capable of opening the blood-brain barrier to allow transport of pharmaceutical agents to the brain. Few of these methods are capable of selectively opening the blood-brain barrier only in the abnormal brain tissue while leaving the blood-brain barrier in the normal brain tissue intact.
For example, Neuwelt et al. used an intracarotid injection of hypertonic mannitol to osmotically disrupt the blood-brain barrier. They reported that this enhanced the uptake by brain tissue of inactivated HSV-1 particles that were administered immediately afterward by intracarotid bolus injection. (E. A. Neuwelt et al., Delivery of ultraviolet-inactivated 35S-herpesvirus across an osmotically modified blood-brain barrier, J. Neurosurg. 74(3):475–79 [1991]; Also, S. E. Doran et al., Gene expression from recombinant viral vectors in the central nervous system after blood-brain barrier disruption, Neurosurgery 36(5):965–70 [1995]; G. Nilaver et al., Delivery of herpesvirus and adenovirus to nude rat intracerebral tumors after osmotic blood-brain barrier disruption, Proc. Natl. Acad. Sci. USA 92(21):9829–33 [1995]).
Intracarotid infusion of leukotriene C4 (LTC4) selectively increases the permeability in brain tumor capillaries without affecting the permeability in normal brain capillaries. The effect of LTC4 on brain tumor capillaries is, however, limited to small molecules and it can only slightly increase the permeability of those small molecules in abnormal brain tissue relative to normal. Accordingly, LTC4 does not significantly increase the delivery of some larger water soluble molecules to brain tumors or other abnormalities.
The vasoactive nonopeptide bradykinin and agonists or polypeptide analogs thereof (e.g., receptor-mediated permeabilizers [RMPs]) have been injected intravenously to increase blood-brain barrier permeability to co-administered neuropharmaceutical or diagnostic agents. (B. Malfroy-Camine, Method for increasing blood-brain barrier permeability by administering a bradykinin agonist of blood-brain barrier permeability, U.S. Pat. No. 5,112,596; J. W. Kozarich et al., Increasing blood brain barrier permeability with permeabilizer peptides, U.S. Pat. No. 5,268,164). Intracarotid infusion of bradykinin will selectively increase permeability 2- to 12-fold in brain tumor and ischemic brain capillaries for molecules ranging in molecular weight from 100 to 70,000 Daltons (Inamura, T. et al., Bradykinin selectively opens blood-tumor barrier in experimental brain tumors, J. Cereb Blood Flow Metab. 14(5):862–70 [1994]). Bradykinin does not increase permeability in the normal blood brain barrier except at very high doses. (Wirth, K. et al., DesArg9-D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (desArg10-[Hoe140]) is a potent bradykinin B1 receptor antagonist, Eur. J. Pharmacol. 205(2):217–18 [1991]). Opening of the blood-tumor barrier by bradykinin is transient, lasting 15 to 20 minutes. (Inamura et al. [1994]). After opening of abnormal brain capillaries with bradykinin, the capillaries become refractory to the bradykinin effect for up to 60 minutes. (Inamura et al [1994]).
A method for selectively delivering to abnormal brain tissue a neuropharmaceutical agent (e.g., 5-fluorouracil, cisplatin, methotrexate, or monoclonal antibodies) or a diagnostic agent (e.g., technicium-99 glucoheptonate, gallium-EDTA, and ferrous magnetic or iodinated contrasting agents) employed intracarotid infusion of bradykinin, or a bradykinin analog, such as RMP-7; the bradykinin or bradykinin analog was administered approximately contemporaneously with the agent. (K. L. Black, Method for selective opening of abnormal brain tissue capillaries, U.S. Pat. Nos. 5,527,778 and 5,434,137). Enhanced transvascular delivery of HSV-derived viral particles to malignant cells in the brains of rats was also achieved by disrupting the blood-brain barrier with bradykinin or RMP-7. (N. G. Rainov, Selective uptake of viral and monocrystalline particles delivered intra-arterially to experimental brain neoplasms, Hum. Gene. Ther. 6(12):1543–52 [1995]; N. G. Rainov et al., Long-term survival in a rodent brain tumor model by bradykinin-enhanced intra-arterial delivery of a therapeutic herpes simplex virus vector, Cancer Gene Ther. 5(3):158–62 [1998]; F. H. Barnett et al., Selective delivery of herpes virus vectors to experimental brain tumors using RMP-7, Cancer Gene Ther. 6(1):14–20 [1999]).
The calcium-activated potassium channel (KCa) is an important regulator of cerebral blood vessel tone (Nelson M T, Quayle J M. Physiological roles and properties of potassium channels in arterial smooth muscle, Am. J. Physiol. 268(4 Pt 1): C799–822[1995]). The KCa channel is ubiquitously distributed in tissues as α and β subunits. Its activity is triggered by depolarization and enhanced by an increase in cytosolic calcium di-cation (Ca2+). A local increase in Ca2+ is sensed by the extremely sensitive brain α-subunit of the KCa, directed towards the cytoplasm in the cell, that allows a significant potassium cation flux through these channels.
Under conditions when intracellular cyclic 3′, 5′ adenosine monophosphate (cAMP) concentration rises in vascular endothelium (e.g. hypoxia), ATP-sensitive potassium channels (KATP) may also play a role. (J. E. Brian et al., Recent insights into the regulation of cerebral circulation, Clin. Exp. Pharmacol. Physiol. 23(6–7):449–57 [1996]). Minoxidil sulfate and chromakalim are reported to be activators of KATP. (A. D. Wickenden et al., Comparison of the effects of the K(+)-channel openers cromakalim and minoxidil sulphate on vascular smooth muscle, Br. J. Pharmacol, 103(1):1148–52 [1991]).
Treatments directed to the use of potassium channel activators or agonists have been taught for disorders including hypertension, cardiac and cerebral ischemia, nicotine addiction, bronchial constriction, and neurodegenerative diseases, but not particularly for the treatment of malignant tumors. (Erhardt et al., Potassium channel activators/openers, U.S. Pat. No. 5,416,097; Schohe-Loop et al., 4,4′-bridged bis-2,4-diaminoquinazolines, U.S. Pat. No. 5,760,230; Sit et al., 4-aryl-3-hydroxyquinolin-2-one derivatives as ion channel modulators, U.S. Pat. No. 5,922,735; Garcia et al., Biologically active compounds, U.S. Pat. No. 5,399,587; Cherksey, Potassium channel activating compounds and methods of use thereof, U.S. Pat. No. 5,234,947).
Bradykinin is thought to increase [Ca2+]i and thus may activate KCa channels. While some other known activators of KCa do not act as vasodilators, for example, 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619; M. Holland et al., Effects of the BKCa channel activator, NS1619, on rat cerebral artery smooth muscle, Br J Pharmacol, 117(1): 119–29 [1996]), evidence is accumulating that KCa may play an important role in vasodilatation mediated by vasodilators, such as bradykinin, NO-donors, cGMP, and guanylate cyclase activators. (Berg T., Koteng O., Signaling pathways in bradykinin-and nitric oxide-induced hypotension in the normotensive rat; role of K+-channels, Br. J. Pharmacol.;121(6):1113–20 [1997]; Bolotina, V. M. et al., Nitric oxide directly activates calcium-dependent potassium channels in vascular smooth muscle, Nature 368(6474):850–3 [1994]; Robertson, B. E., et al., cGMP-dependent protein kinase activates Ca-activated K channels in cerebral artery smooth muscle cells, Am. J. Physiol. 265(1 Pt 1):C299–303 [1993]; Sobey, C. G. et al., Mechanisms of bradykinin-induced cerebral vasodilatation in rats. Evidence that reactive oxygen species activate K+ channels, Stroke 28(11):2290–4; discussion 2295 [1997]; C. G. Sobey and F. M. Faraci, Effect of nitric oxide and potassium channel agonists and inhibitors on basilar artery diameter, Am. J. Physiol. 272(1 Pt 2):H256–62 [1997]).
Bradykinin's action as a powerful vasodilator is disadvantageous when using bradykinin to open the blood-brain barrier to therapeutic anticancer agents. Bradykinin or its analogs may adversely lower blood pressure, reduce cerebral blood flow, or contribute to brain edema in some patients. (E.g., A. M. Butt, Effect of inflammatory agents on electrical resistance across the blood-brain barrier in pial microvessels of anesthetized rats, Brain Res. 696(1–2):145–50 [1995]). In addition, bradykinin constricts smooth muscle and stimulates pain receptors.
Consequently, there is still a definite need to maximize the effectiveness of a wide variety of therapeutic agents through enhanced selective transvascular delivery to malignant tumors, including those of the central nervous system, and/or to other abnormal brain regions. These and other benefits the present invention, employing potassium channel agonists, provides as described herein.